The behaviour of platinum-group elements in basalts from the East Greenland rifted margin

被引:104
作者
Momme, P
Tegner, C
Brooks, CK
Keays, RR
机构
[1] Aarhus Univ, Inst Geol, DK-8000 Aarhus C, Denmark
[2] Danish Lithosphere Ctr, DK-1350 Copenhagen, Denmark
[3] Univ Copenhagen, Inst Geol, DK-1350 Copenhagen K, Denmark
[4] Monash Univ, Dept Earth Sci, Clayton, Vic 3168, Australia
关键词
D O I
10.1007/s00410-001-0338-1
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The continental flood basalts of the East Greenland volcanic rifted margin were extruded during continental breakup above the ancestral Iceland mantle plume at 55 Ma. Three distinct magma types, the low-Ti, high-Ti and very high-Ti series (LTS, HTS and VHTS respectively), are found intercalated in the similar to6-km-thick Plateau Lava sequence. Incompatible trace elements indicate that the LTS are derived from a more depleted mantle source compared to HTS and VHTS. The LTS is characterised by increasing Cu (105 to 248 ppm) and Pd (7 to 24 ppb), constant Cu/Pd ratio (similar to10,000), and decreasing Ir (1.1 to < 0.05 ppb) and Ru (1.8 to < 0.3 ppb) concentrations during magmatic differentiation (16 to 7 wt% MgO). The constant Cu/Pd ratio reflects silicate- and chromite-dominated fractionation without concurrent segregation of sulphide. S-undersaturated differentiation is also indicated in the HTS, which also displays increasing Pd (6-16 ppb) and decreasing Ir concentrations (I to < 0.05 ppb) during differentiation, and the Cu/Pd ratios for the entire series average 21,000. However, some HTS samples have elevated Cu/Pd ratios (up to 33,000). Cu/Pd ratios in the HTS do not correlate with MgO, and this is interpreted to reflect varying Cu/Pd ratios of HTS parental magmas rather than S-saturated differentiation. During S-undersaturated differentiation of the LTS and HTS, Pt/Pd ratios decrease from 1.3 to 0.11 and 1.1 to 0.2 respectively, which indicates that Pd is much more incompatible than Pt during S-undersaturated differentiation. The VHTS consists exclusively of highly evolved samples with low MgO (6.6-6.1 wt%) and Pd/Ir ratios 98-228. Here, Cu/Pd ratios increase from 17,500 to 35,000 with decreasing Cr concentrations which indicate that these magmas experienced silicate fractionation with concurrent segregation of sulphide. The LTS represent melting of a depleted source and show high PGE concentrations and constant Cu/Pd ratios during S-undersaturated differentiation. Melting of a normal depleted upper mantle source generates S-saturated melts (MORB), and the depleted LTS source is therefore considered an extraordinary S-poor component within the ancestral Iceland plume. Of the three series, the VHTS contain the largest contribution from enriched mantle portions. The VHTS have similar PGE but much higher Nb concentrations for instance compared to the most evolved LTS and HTS samples, indicating that the enriched source contributes Nb but not PGE.
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页码:133 / 153
页数:21
相关论文
共 65 条
[51]   GEOLOGY, GEOCHEMISTRY, AND ORIGIN OF PLATINUM-GROUP ELEMENT CHROMITITE OCCURRENCES IN THE HEAZLEWOOD RIVER COMPLEX, TASMANIA [J].
PECK, DC ;
KEAYS, RR .
ECONOMIC GEOLOGY AND THE BULLETIN OF THE SOCIETY OF ECONOMIC GEOLOGISTS, 1990, 85 (04) :765-793
[52]   Structure and stratigraphy of the Early Tertiary basalts of the Blosseville Kyst, East Greenland [J].
Pedersen, AK ;
Watt, M ;
Watt, WS ;
Larsen, LM .
JOURNAL OF THE GEOLOGICAL SOCIETY, 1997, 154 :565-570
[53]   Platinum-group elements (PGE) in basalts of the seaward-dipping reflector sequence, SE Greenland coast [J].
Philipp, H ;
Eckhardt, JD ;
Puchelt, H .
JOURNAL OF PETROLOGY, 2001, 42 (02) :407-432
[54]   Ir, Ru, Pt, and Pd in basalts and komatiites:: New constraints for the geochemical behavior of the platinum-group elements in the mantle [J].
Rehkämper, M ;
Halliday, AN ;
Fitton, JG ;
Lee, DC ;
Wieneke, M ;
Arndt, NT .
GEOCHIMICA ET COSMOCHIMICA ACTA, 1999, 63 (22) :3915-3934
[55]   OLIVINE-LIQUID EQUILIBRIUM [J].
ROEDER, PL ;
EMSLIE, RF .
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 1970, 29 (04) :275-&
[56]  
Saunders A.D., 1997, GEOPHYS MONOGRAPH SE, P45, DOI 10.1029/GM100p0045
[57]   40Ar/39Ar geochronology of Tertiary mafic intrusions along the East Greenland rifted margin: Relation to flood basalts and the Iceland hotspot track [J].
Tegner, C ;
Duncan, RA ;
Bernstein, S ;
Brooks, CK ;
Bird, DK ;
Storey, M .
EARTH AND PLANETARY SCIENCE LETTERS, 1998, 156 (1-2) :75-88
[58]   Evidence from the rare-earth-element record of mantle melting for cooling of the tertiary Iceland plume [J].
Tegner, C ;
Lesher, CE ;
Larsen, LM ;
Watt, WS .
NATURE, 1998, 395 (6702) :591-594
[59]   Platinum-group minerals in chromitites from the Ojen Iherzolite massif(Serrania de Ronda, Betic Cordillera, Southern Spain) [J].
TorresRuiz, J ;
Garuti, G ;
Gazzotti, M ;
Gervilla, F ;
HachAli, PF .
MINERALOGY AND PETROLOGY, 1996, 56 (1-2) :25-50
[60]  
Tredoux M., 1995, S AFR J GEOL, V98, P157